Campbell Scientific SDM-INT8 8-Channel Interval Timer - Manual (Page 19)

SDM-INT8 8 Channel Interval Timer
Channel 1: frequency (2)
Channel 3: counts on channel 2 since channel 1 (5)
Channel 4: frequency (2)
Channel 5: time since previous Channel (3)
Channel 2,6,7,8: none (0)
Channel 1: RPM may be calculated from crankshaft frequency.
Channel 3: Flywheel teeth count between the crankshaft reference
pulse, and the spark gives reference to the crank angle.
Channel 4: The frequency of fuel injection may be multiplied by
channel 5's positive pulse width to yield fuel injector duty
cycle. The multiplication is not performed in the INT8.
Channel 5: Time of the positive pulse width of the fuel injector is given
in milliseconds.
6.4 Output Option
An important conceptual difference between Output Options and Functions is
that one Output Option is selected per Instruction (SDMINT8 or Instruction
101) and applied to data from all channels. Functions are applied to individual
channels.
6.4.1 Rules for Averaging
This Section applies to only those Output Options which perform averaging
(i.e., 0, 32768, nnnn in SDMINT8 or 0, 0--, XXXX in Instruction 101).
Averaging is performed on events which are defined by at least two edges. For
example, to average a period two rising edges are required to define a period.
To average the time since the previous channel, an edge on the previous
channel followed by an edge of the channel programmed for time since
previous channel is required.
No averaging is done on channels programmed for Function 7, "Counts".
Channels programmed for counts do not require two edges for an event.
Single edges of the specified direction are counted.
The maximum interval that the INT8 can time is 16.77 seconds. Edges which
are separated by a time longer than this will result in a false measurement.
In all Output Options that average, the INT8 is storing measurements and
processing. The measuring/storing task takes priority over the processing task.
If the input signal exceeds a certain frequency, processing will lag behind
measuring/storing. Table 3 provides the maximum average frequency at which
the processing task keeps up with the measuring/storing task.
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